1. Field of the Present Invention
The present invention relates to pressure transducers and more particularly to pressure transducers employing strain gages.
2. The Prior Art
A variety of pressure transducers have been developed in the prior art, several of which employ plural active strain gages in a bridge circuit, along with passive elements which are responsive to temperature but not strain, in order to effect a temperature compensation. One such transducer is described in Swiss Pat. No. 549,794. While such prior art transducers are effective to reduce the effect of variation of temperature, they do not attempt to compensate for other error signals and display a large hysteresis, and so the attainable resolution is quite poor. They are not suitable for vacuum operation, and therefore cannot be leak-checked with the most accurate leak-checking techniques. They are also unsuitable for use in conditions of low temperature or high pressure.
Some of the pressure transducers known in the prior art also suffer from one or more of a variety of other disadvantages, including the need for a feed through capability to permit a strain gage mounted on one side of a surface to transmit a signal to the other side of the surface, and the need for movable seals or sealing mechanisms for sealing against the pressure being measured. These disadvantages are especially critical when the pressure transducer is to be used with toxic or radioactive gas or fluids. Special care is required to prevent leakage when the seals wear out or otherwise fail.
Another disadvantage of some pressure transducers is the tendency to produce output signals which vary in steps instead of continuously, which introduces hysteresis and limits the resolution of which such transducers are capable. Such hysteresis is generally caused by sliding seals or friction in mechanical linkages.
Another disadvantage of prior art pressure transducers is that they produce a relatively weak or low amplitude signal for a given change in pressure, so that resolution is also limited because of the signal-to-noise ratio of the output of the transducer.
Still another disadvantage of many prior art pressure transducers is that they must be connected to the vessel containing the fluid whose pressure is measured by means of flanges and fittings with seals or the like, and cannot be welded into place.
Also, some pressure transducers are not capable of responding quickly and accurately to changes in pressure, but produce a ringing or oscillating output signal in response to sudden pressure changes.